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A double-sided polished photonic crystal fiber (DP-PCF) for surface plasmon resonance(SPR) sensing is designed and analyzed by using the finite element analysis software COMSOL 5.5. The suggested design shows strong sensitivity stability in the low refractive index (RI) region ( $1.33\sim 1.39$ ) and ultra-high sensitivity in the high RI region ( $1.39\sim 1.43$ ), respectively. The structural parameters of the proposed sensor are studied to analyze the stability and high sensitivity of the fiber sensor. The introduced DP-PCF sensor offers high sensitivity of 32,434 nm/RIU in the RI range of $1.39\sim 1.43$ due to its special double-sided polishing design.

In this paper, we demonstrate a high sensitivity refractive index (RI) sensor with D-shaped structure covered with gold and graphene film. Specifically, the effect of structural parameters on the stability of fiber sensor is analyzed. In our research, it have been found that the sensor we proposed is not very sensitive to the change of structure parameters on the premise of ensuring the sensing precision. This advantage means that the requirements for machining errors are reduced. Further probing shows that the proposed sensor shows a maximum wavelength interrogation sensitivity of 4391nm/RIU with the dynamic refractive index range from 1.33 to 1.39 and a maximum amplitude sensitivity of 1139RIU− 1 with the analyte RI = 1.38 in the visible region. The corresponding resolution are 2.28 × 10− 5 and 8.78 × 10− 6 based on the methods of wavelength interrogation and amplitude-(or phase-) based method. These characteristics of compact sensing architectures, simple to fabricate, and high sensitivity open the possibility of using this type of sensor in biological applications.

We propose and investigate a photonic crystal fiber (PCF) refractive index sensor with triangular lattice and four large-size channels based on surface plasmon resonance. In such sensor, two gold wires obtained by chemical reaction are filled in two air holes between the upper and lower channels. Numerical results show that the refractive indexes of the analytes can be detected from 1.30 to 1.79. It’s a very broad detection range that is rarely seen in the field of photonic crystal fiber sensor based on surface plasmon resonance. The average sensitivity of this photonic crystal fiber could be 100 nm/refractive index unit (RIU) in the dynamic index range from 1.30 to 1.63. In the range from 1.63 to 1.79, the highest sensitivity could reach to 3233 nm/RIU. The ability to integrate four large-size microfluidic channels for efficient analyte flow in is attractive for the development of integrated highly sensitive PCF-SPR sensors.

A polarization filter at the two communication windows of 1.31 and 1.55 μm based on photonic crystal fiber (PCF) coated by nanoscale gold film is proposed. The effects of geometrical parameters of the PCF on the performances of polarization filter are evaluated by finite element method (FEM). Numerical simulations reveal that the polarization filter possesses ultra-short length of 400 μm and high extinction ratios of 41 and −150 dB at the communication wavelengths of 1.31 and 1.55 μm respectively. The bandwidth of extinction ratio (ER) better than 20 dB is 58 nm at the communication window of 1.31 μm. Moreover, the bandwidth of ER better than −20 dB is 164 nm at the communication window of 1.55 μm.

We propose a modified design for a photonic crystal fiber (PCF) filter based on surface plasmon resonance(SPR). The air holes are arrayed in rectangular lattices, while the size and the pitches of holes around the gold-coated holes are different. That can separate the x-polarization and y-polarization of second-order surface plasmon polariton (SPP). The resonance strength of the surface plasmon mode and import of structural parameters of the PCF on the filter characteristics are studied through using the finite element method (FEM). Numerical simulations demonstrate that the thickness of the gold layer, the gold-coated or gold-filled, and the asymmetry around the gold-coated holes have a great effect on the filter characteristics. It is certain to obtain a resonance strength as high as 873 and 771.5 dB/cm at the communication wavelength of 1050 and 1310 nm in x-polarization by adjusting the size and the place of the gold-coated holes, while the loss is extremely low in y-polarization.

The polarization filter characters of a square lattice photonic crystal fiber with a large diameter gold-coated air hole are studied by finite element method. Results show that the resonance strength of y-pol direction is far stronger than x-pol direction. It can achieve 517 and 375 dB/cm, respectively, in y-pol direction at the communication wavelengths of 1310 and 1550 nm by adjusting structural parameters. If a second large hole is added in the opposite corner of the lattice, the resonance strength of y-pol direction can increases to 701 dB/cm at 1310 nm. At the same time, the influence for polarization filter characters is studied by changing the fiber length, the thickness of gold layer, the diameter of large air hole, and the diameters of small air holes.

A broadband single-polarization photonic crystal fiber polarized filter based on surface plasmon resonance is proposed based on finite element method. Numerical simulations show the confinement loss of y-PCM (y-polarized core mode) is much higher than that of x-PCM (x-polarized core mode) in the wavelength range 1.20–1.63 μm. The confinement loss of y-polarized mode is 45,240 and 10,200 dB/m at the communication wavelength 1.31 and 1.55 um, respectively, and the corresponding loss of x-polarized mode is just 90 and 80 dB/m. When the fiber length is 3 mm, the bandwidth of extinction ratio better than -20 dB is greater than 430 nm covering almost all the communication wavelength. To our best knowledge, the bandwidth is the widest. The impacts of structural parameters on the resonance characteristics are also discussed. The structure could be further optimized for better result.

In this paper, a novel D-shaped photonic crystal fiber (D-PCF) based on surface plasmon resonance (SPR) is designed, and gold nanowire is used as the SPR active metal. A full-vector finite element method is applied to analyze the polarization filter characteristics. Phase matching between the second-order surface plasmon polariton (SPP) mode and the core-guided modes of x- and y-polarization can be met in two different wavelengths. By adjusting the diameters of the large air holes and the gold nanowire, this designed D-PCF can be used to the polarization filter in two communication bands. The loss of unwanted y-polarization mode can reach 244.9 and 292.8 dB/cm at the wavelength of 1.31 and 1.55 μm, respectively. With a length of 1 mm of the designed D-PCF, the bandwidths with the crosstalk better than 30 dB can reach to 88 and 150 nm, and the crosstalks are 208.4 and 249.5 dB the wavelength of 1.31 and 1.55 μm, respectively.

A novel polarization splitter based on d-shaped dual-core photonic crystal fiber with gold film is proposed and analyzed by the finite element method. The designed polarization splitter involves side-polishing of photonic crystal fiber and depositing of gold film. The numerical results reveal that the separate length is 0.782 mm and the extinction ratios are -151 and -55 dB for the x- and y-polarized modes at the communication wavelength of 1,550 nm. The bandwidths of the polarization splitter are 40 and 65 nm for the x- and y-polarized modes with extinction ratios better than -20 dB and insertion losses lower than 0.3 dB. This d-shaped dual-core photonic crystal fiber is competitive for polarization splitter.

We propose and investigate a D-shaped photonic fiber refractive index sensor with rectangular lattice based on surface plasmon resonance. In such sensor, the nanoscale gold metal film is deposited on the flat surface where it is side polished. Numerical results show that the average sensitivity of Au-metalized surface plasmon resonance (SPR) sensor could reach as high as 8,129 nm/refractive index unit (RIU) in the dynamic index range from 1.35 to 1.41 as well as 2,000 nm/RIU from 1.33 to 1.35. Compared to conventional Au-metalized SPR sensors, the performance of our device is obviously better, and the production process is greatly simplified.